Block 3 - Muscle Tissue Flashcards Preview

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Flashcards in Block 3 - Muscle Tissue Deck (64):

What are the two most important characteristics of muscle tissue?

Contractility and conductivity


What are the three major types of muscle?

Skeletal, smooth, and cardiac


Which muscle types are involuntary?

Smooth and cardiac


What muscle types show striations?

Skeletal and cardiac


Where are each of the three types of muscle predominantly found?

Skeletal - skeleton and visceral (tongue, pharynx, upper part of esophagus, aiding with swallowing and speech)


What are the special terms for the plasma membrane, cytoplasm, and SER in muscle cells?

Sarcolemma, sarcoplasm, and sarcoplasmic reticulum


Where do skeletal muscle fibers originate from? How do these arrange themselves?

Myoblasts fuse to form long multinucleated postmitotic myotubes


What is a muscle "cell" made up of?

Multinucleated syncytium, forming a skeletal muscle fiber


What forms t-tubules? Where to t-tubules extend? Why?

Extend into cytoplasm to carry depolarization deep into sarcoplasm


Where are nuclei of skeletal muscles located?

Peripherally, immediately beneath the sarcolemma


What are the three most important structures located in the sarcoplasm of a muscle cell?

Myofibrils, filamentous mitochondria, and myoglobin


What does the sarcoplasmic reticulum store? When this substance is released, what does it cause?

Ca++, a muscle contraction


What is the organization of skeletal muscles?

Thick and thin filaments for a myofibril
Myofibrils extend end to end to form a muscle fiber
Fascicles are formed by groups of muscle fibers
Groups of fascicles form a skeletal muscle


What are thin filaments composed of? What are the structure/roles of each?

F-actin - double stranded helical filament
Tropomyosin - filament that lies in groove of two actin monomes
Troponin complex - T: binds to tropomysoin anchoring complex, I: binds to actin to inhibit interaction with myosin, C: smallest, binds C++ which initiates muscular contraction


What are thick filaments composed of? What does the subunit consist of?

Myosin (II), consisting of two heavy chains a-helices and two globular heads. Two pairs of light chains attached to the heads


What is contained in the A-band region?

Both thick and thin filaments


What is contained in the H-zone region?

Thick filaments


What is special about the M-line?

Formed by accessory proteins that hold thick filaments together


What is contained in the I-zone region? What bisects it?

Thin filaments. The Z-disk.


What are the two main functions of the z-disk?

Provides anchoring points for thin filaments and supports architecture of the myofibril


What is the basic contractile unit of skeletal muscle?



Why do skeletal muscles have cross striations?

The sarcomeres of individual myofibrils are in register


Which zones change length during a muscle contraction? Which one does not? Why?

The I-band changes length as the distance between the thick filaments and the z-disk decreases
The H-band changes length as the thin filaments encroach on the m-line.
The A-band does not change length as the thick filaments do not change length.


Where are accessory proteins primarily found in the sarcomere?

The z-disk and the m-line


What are the 6 types of accessory proteins in a muscle cell?



Which two accessory proteins are associated with the thick filaments? What do they do?

Myomesin - hold thick filaments in register at m-line
Titin - found primarily near z-disk, anchoring thick filaments to z-disks keeping them in center of sarcomere


What 4 accessory proteins are associated with thin filaments? What do each do?

A-actinin - anchors thin filaments to z-disk
Nebulin - run parallel to thin filaments, attaching to z-disk. Regulates length of thin filaments during a contraction
Desmin - Intermediate filament forming lattice around z-disk, attaching z-disk to one another and plasma membrane
Dystrophin - Membrane associated protein complex that attaches actin cytoskeleton to extracellular matrix


How fast can an action potential travel down a muscle cell?

120 m/s


What composes one membrane triad?

One T-tublule and two cisternae of sarcoplasmic reticulum


Is the T-tubluar system deep or shallow? Why?

The T-tubular system is deep invaginations of sarcolemma to allow the action potential to travel deep into the muscle cell


What are terminal cisternae? Where do they run in relation to a muscle fiber?

Sarcoplasmic reticulum containing high concentrations of Ca+, running near the A-band/I-band boundary


What are the steps of a muscle contraction?

1) At rest, tropomyosin covers the myosin binding sites on actin
2) When Ca++ binds to Troponin C, conformational change elicited
3) Tromopyosin shifts, opening myosin bindign sites on actin
4) Myosin walks along actin, using ATP to slide along.


In relation to ATP, what is myosin considered to be? Why?

ATPase because it uses ATP energy to slide along actin


How is a skeletal muscle relaxed?

1) Ca++ pumps begin to pump Ca++ back into sarcoplasmic reticulum
2) Ca++ unbinds from Troponin C, causing conformational change
3) Tropomyosin covers the myosin binding sites on actin


How are skeletal muscles regenerated? What does extensive damage cause?

Through satellite cells, proliferating to give rise to new myoblasts, fusing to become new muscle fiber. Extensive damage causes CT scar


What are three ways muscles change shape over a lifetime? What are each caused by?

Increase diameter - result of aging
Hypertophy - result of exercise
Atrophy - disuse


Name the three layers of CT in skeletal muscle? What does each surround?

Endomysium - reticular fibers surrounding individual muscle fibers
Perimysium - thicker collagenous CT surrounding muscle a fascicle
Epimysium - thick CT surrounding group of fasicles


What are the three main characteristics of smooth muscle?

Contractile filaments ill-organized, causing no striations
Rhythmic/slow/prolonged contractions (can be rapid aka eye)


As opposed to skeletal muscle nuclei located on the periphery of a cell, where are smooth muscle cell nuclei located? What is their shape

In the center, long cigar shaped with tapered ends


How are smooth muscle filaments organized?

Thin filmanets anchored to dense bodies, whicha re formed by a-actinin. Dense bodies are anchored to desmin network. Thick filaments are scattered thorughout sarcoplasm.


What is the analog of z-disks in smooth muscle?

Dense bodies


How do individual muscles cells communicate in smooth muscle?

Communicating (gap) junctions


What are caveolae-live invaginations? What is their purpose?

Invaginations of sarcolemma into the cell to transmit depolatization to chambers of sacoplasmic reticulum, located beneath caveolae


What surrounds/encloses smooth muscle cells, playing an important role in force transduction?

Basil lamina and a network of reticular fibers


Describe contractile filaments of smooth muscle cells and how they are different from skeletal muscle

No troponin complex, caldesmon smooth muscle specific actin binding protein, masking the myosin-binding sites


Myosin binds to actin in smooth muscle only when what occurs?

Myosin is phosphorylated


What is the resting/inactive form of myosin in smooth muscle?



How are smooth muscle cells excited?

Antonomic nervous system's post ganglionic fibers
Neurotransmitters diffuse through CT, impacting many cells
Not all receive terminal nerves, and are therefore receive impulses through gap junctions


Besides neural, what two other types of stimulation can elicite a response from smooth muscle?

Chemical and mechanical (passive stretching can lead to initiation of muscular contraction)


What are the steps of smooth muscle contraction?

1) Ca++ released into sarcoplasm from sarcoplasmic reticulum
2) Ca++ binds to calmodulin, creating a complex. This binds to caldesmon, releasing it from actin and opening myosin-binding site on F-actin
3) Ca++-calmodulin activates myosin light-chain kinase
4) Myosin light-chain kinase phosphoylates regulatory light chain of myosin molecule
5) Phophorylated light chain unfolds myosin and actin-binding site on head is exposed to actin
6) Cell shortens, nucleus folds into corkscrew shape


Describe the events of smooth muscle relaxation

1) Ca++ pumped into sarcoplasmic reticulum
2) Calmodulin disassociates from light chain kinase
3) Myosin dephosphorylated, becoming inactive
4) Caldesmon binds to myosin binding site on actin filament
Slow action, prolonged effect


What is latch state? Why does it have that name?

Secondary mechanism that allows long term contractions with minial expenditure of energy. Caused by decrease of ATP activity while myosin head is bound to actin


Whaat contributes to tone of blood vessels? What does this resemble in skeletal muscles?

Latch state, rigor mortis


Name 3 main places smooth muscle is located in the body

Walls of hollow organs (Blood vessels/Lymph system
Large ducts/glands
GI tract
Reproductive tract
Urinary system)
Iris and ciliary body
Dermis of skin (attached to hair follicles)


Describe the blood supply and regeneration of smooth muscle

Moderate blood supply thorugh capillaries and CT directly around muscle cells
Active regenerative response - undergo mitosis and replace damaged or lost cells


What are 4 major characteristics of cardiac muscle?

Extensive blood supply
No ability for regeneration


How do cardiac muscle fibers differ from skeletal muscle fibers?

Formed by individual cells, whereas skeletal muscle fibers are formed by a syncytium of myofibrils


What features of a cardiac muscle cell nucleus resemble a smooth muscle cell nucleus? How are they different?

The nucleus is centrally place, but round instead of cigar shaped and taperd


How is branching formed in cardiac muscle? Is it seen in other types of muscle?

When two muscle cells attach to end of one muscle cell, branching occurs. And no.


What is the connection between two individual cells called?

Intercalated disks


What two portions of the intercalated disks contain the different types of junctions? Which types of junctions are contained on each?

Transverse Portion - containing anchoring junctions for stability (adherens junctions and desmosomes)
Lateral Portion - parallel to myofilaments, containign communicating junctions


Where are T-tubules found in cardiac muscle? Are they small or large?

Large, found at z-disks


Why to cardiac muscle cells only have diads?

Sarcoplasmic reticulum isn't as well developed, only on one side of a T-tubule


What fibers initiate, coordinate, and regulate the heartbeat of the cardiac system?

Purkinje fibers, forming nodes and bundles including sinoatrial and atroventribular nodes, and the bundle of His